can you please suggest what I can do to troubleshoot this issue?
Ken,
Let me try to give you suggestions of what I would have tried in your situation.
First, to make sure I understood correctly: you access this e-mail account only via 3 ways: (1) from your phone and (2) from tablet, with Aquamail on both set to connect via IMAP, and (3) occasionally via Webmail interface. Right?
No other computers, devices, apps on the same phones (e.g. stock app originally configured to connect and later abandoned but still running), backup connections, etc.
Correct?
Does it happen always, or only sometimes?
(If it happens always, - that should mean that
all messages in your account are
read, except for the first very few moments after they arrived. Is that the case?)
In that case, here is what I would do for testing (temporarily):
1. Turn off the sync in Aquamail for the account in question on both devices (both scheduled sync and PUSH, if enabled). Log in via your webmail interface, and watch what happens to the status of the new message when it comes in, a few minutes after that (obviously, you'd need to reload your webmail window).
(You can send yourself a message from a different account.)
If the state has changed, - that means that either your server changes it, or something else accessing your account.
To Turn Off the sync in Aquamail for the specific account, follow this procedure:
Long Press on the account name (in the account view) -> Options and folders -> Account options -> Scheduled sync -> UNCHECK.
-> IMAP Push -> UNCHECK
Please, use this way so that you can run the test #3 (below) without interference.
If you see the state not changing after a few minutes of the message arrival:
2. Set up a different Mail program to access this e-mail account via IMAP. I'd personally suggest Thunderbird on a computer, but if you don't have access to a desktop/laptop, you can try using your stock app on the tablet.
Once it is set up and is receiving mail, send again a test message to this account from another one, let this program sync, do not open the message, and watch if the message status changed.
If it did, it means that your ISP server changes the status of the message upon it being downloaded via IMAP. (This would be weird) - You'd need to contact your ISP for further questions about "why", and "how that can be disabled".
If that state didn't change, try
3. Create a new Aquamail IMAP account on one of your devices, - for the same ISP account.
Do not change
any options.
Repeat the test is in 2. above.
See if the state of the message changes after Aquamail re-syncs.
If the state of the message does not change, and you've done everything as described above, - it means that something is messed up with the configuration/settings on your existing accounts in Aquamail. You can use the newly created account instead and tune your settings paying attention to what you might be changing in the process. (Although I cannot think of any settings that would do this... But maybe I am missing something)
In case the state does change in this case (and it didn't in #2), - you may want to get back here, and let Kostya know, and at that point you might need to catch the behavior in the debug log.
But I actually doubt you'd get to the Test #3.